1. Energy Research Institute (ERI@N), Interdisciplinary Graduate School, Nanyang Technological University, 637553, Singapore
2. Helmholtz Institute Ulm (HIU), Ulm 89081, Germany
3. Physics Department, Faculty of Science, National University of Singapore, 117542, Singapore
4. Karlsruhe Institute of Technology (KIT), Karlsruhe 76021, Germany
5. School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore
6. School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore